Chapter 42 Nuclear Physics

A photograph of the detector of the Large Hadron Collider.

This detector at the Large Hadron Collider probes the structure of protons and searches for the ultimate building blocks of matter.

In This Chapter, you will learn about the nucleus and some applications of nuclear physics.

What is the structure of an atomic nucleus?

You will learn how the nucleus is constructed and what holds it together.

  • The nucleus consists of protons and neutrons. Both are known as nucleons.

  • The diameter of the nucleus is only a few femtometers.

The figure illustrates an atom and its nucleons.

《 LOOKING BACK Sections 37.6–37.7 The nucleus

Can quantum mechanics explain the nucleus?

The nucleus is held together by a new force of nature, the strong force.

  • The strong force is a short-range force.

  • A quantum shell model for nucleons, analogous to the electron shells in atoms, explains many nuclear properties.

The figure illustrates the energy level diagram of the superscript 12 BaseLine C atom.

《 LOOKING BACK Section 40.6 Potential wells

Which isotopes are stable?

More than 3000 isotopes are known, but only 252 have a stable nucleus.

  • In a graph of neutron number versus proton number, the stable nuclei all cluster near a well-defined line of stability.

  • We also see that the number of neutrons grows faster than the number of protons.

The figure illustrates the Stable and unstable nuclei shown on a plot of neutrons versus protons.

What is radioactivity?

Radioactivity is the emission of high-energy particles when unstable nuclei decay.

  • Alpha decay: Emission of a 4He nucleus.

  • Beta decay: Emission of an electron or positron.

  • Gamma decay: Emission of a high-energy photon.

    The figure consists of two parts that illustrate the before and after of alpha decay.

What is a half-life?

The number of unstable nuclei in a sample decreases exponentially with time.

  • The time in which half the nuclei decay is called the half-life of the isotope.

  • Decayed nuclei don’t vanish. They become a different nucleus called the daughter nucleus.

    The figure illustrates the half-life graphically.

How is nuclear physics useful?

The atomic nucleus is surprisingly useful. Nuclear medicine uses weak radioactive isotopes to image the body and strong beams of nuclear radiation to kill tumors. Engineers trace the motions of gases and liquids with radioactive isotopes. Archeologists and geologists date artifacts and lava flows by observing the decay of radiation. Nuclear energy is a significant source of carbon-free electricity. And all the atoms in our bodies other than hydrogen were created billions of years ago by nuclear fusion reactions in a supernova.

Learning Objectives

After studying this chapter, you should be able to

  1. 42.1 Describe nuclear structure.

  2. 42.2 Calculate nuclear binding energies.

  3. 42.3 Work with the strong force.

  4. 42.4 Interpret nuclear energy levels using the shell model.

  5. 42.5 Calculate activity and half-lives for nuclear decay.

  6. 42.6 Compare the types and properties of nuclear radiation.

  7. 42.7 Determine the radiation dose for different types of radiation.